It's obviously a tricky area - and the implications of wetter dough are far reaching.

But, if we focus soley on one aspect, i.e. the structure of the crumb being more open, is there a direct answer to that question.

For example, I realise - we can say things like - more water speeds up the fermentation process - and a very well fermented dough will have more bubbles - and more bubbles will mean more rise - and more rise means a more open crumb. But, for the sake of not losing my sanity - I would prefer to consider that as a topic of conversation to do with fermentation.

Perhaps, I am simplifying things to a point where they almost become meaningless or misleading - but if fermentation (and all other knock on effects of hydration are equal) is there something specific about hydration that will result in a open crumb?

Unfortunately, you really can't talk about hydration in the abstract or in isolation. It is true that using more water with a given weight of flour should produce a softer dough (all else being equal). And that dough should translate into a more open and airy finished crust. But that is only with the right oven and the right bake temperature. For example, in my standard electric home oven with a basic Cordierite stone, I start to have problems with oven spring once the hydration gets above about 65%. The temperature in my oven doesn't get high enough to convert the water in the dough to steam to produce a highly open and airy crust. This limitation has other consequences. For example, it limits the size of the pizzas I can make, the thickness of the crusts of my pizzas, and how much sauce, cheese and toppings (and their types) that I can use. The high hydration will also affect my bake times and getting the pizzas properly baked. High hydration doughs are also harder to handle because of their excessive extensibility and wetness.

Thanks again Peter. I appreciate the point about the oven temperature.

Can you tell me if you agree or not with the sentence below? And if you do - would you say that this is one of the key reasons to use a high hydration dough when cooking at high temperatures?

"One of the consequences of using a high percentage of water in a dough recipe is that we will end up with a softer dough. Softer dough - if cooked at sufficiently high temperatures - will result in a more open crumb structure than less soft dough - because it is easier for the air bubbles in the dough to expand - that is - there is less resistance against their expansion"

I would say that the main reason for using a high hydration value is to achieve a more open crumb structure. A secondary, but still important, reason is that the dough will ferment faster (all else being equal). Neapolitan pizza makers routinely adjust the hydration of their ambient temperature fermented doughs to compensate for seasonal variations. However, they do this by adjusting the amount of flour, not the water, because the amount of water is fixed. The Neapolitan pizzaioli also use yeast quantity and salt quantity to compensate for seasonal variations. You might not need to do these sorts of things where you are in Colombia.

In your quoted paragraph, I would delete the word "air". The bubbles might include some air, and also carbon dioxide, but the principal driver of the oven spring is water in the dough being converted to steam under the influence of the high oven temperature. The gases in the dough will also expand during baking and contribute to oven spring.

Even if I could tweak my recipe and foresee the knock on effects in terms of fermentation - it would be pointless as the weather in Colombia, Medellin is very erratic - it can rain at very short notice - and then there is a massive temperature drop. Sometimes, the sky turns black it looks like itís about to rain - and then the clouds move on - it doesn't rain - and you have blue skies.

As a result - all the fermentation is in a fridge - albiet not a very cold fridge - which with 4 degrees between its top and bottom temperatures - is I imagine - still affected by the outside temp.

Anyway, I totally forgot about the issue of hydration - and the importance of steam in the oven.